Lubricating composition



United States Patent M 2,845,390- LUBRICATING coMPosl'rIoN Paul M. Kerschner, Pennsauken, N. J., assignor to Cities Service Research and Development Company, New York, N. Y.,- a corporation of New Jersey No Drawing. Application February 23, 1956 SerialNo. 567,084

6 Claims. (CL 252-486) This invention relates to lubricating compositions, and more particularly toimproved synthetic lubricant compositions.

Considerable interest has been focused in recent years on the need for improved lubricating compositions which will provide satisfactory lubrication. under increasingly more difiicult operating conditions. The present and increasing use of higher compression internal combustion engines and the anticipated widespread adoption of turbine type engines, both for air and ground use, has made it necessary to have available lubricants which will provide adequate protection for functioning parts under a wide variety of operating conditions. The required compositions must have, in addition to normal viscosity and pour point ranges, minimum. fire and flash points, increased heat stability, oxidation and corrosion. resistance.

Until recently, hydrocarbon oils modified in part by the addition of various types of additives, such as. for example, viscosity improvers and pour point. depressants, have satisfactorily met present day operating conditions. However, the limits to which mineral oil base stocks can be satisfactorily modified by blending and additive treatment will shortly be reached, so that lubricating compositions from a synthesized source seem to be necessary.

In the field of synthetic lubricant development, some success has been obtained with various types of. compounds, including silicones, fiuorinated hydrocarbons, ethers, esters and various combinations of the foregoing. Among these the ester type of compound, particularly those of the dibasic acid type, have been found to possess characteristics making them reasonably well suited to. serve as lubricants; The present invention falls within this field of activity, and is directed to new and improved thioether ester type of synthetic lubricating compositions. The present invention is based on the discovery that if certain specific tetra-basic thioether ester derivatives of itaconic acid are mixed with a small amount of a polymeric ester of the acrylic acid series, the resulting compositions possess unique and unexpected properties which make them suitable as synthetic lubricants. In particular, the new' compositions of this invention are possessed of viscosity indices and pour point characteristics which make them ideally suited for lubricating'purposes. Moreover, the compositions of the present invention" have flash and fire points that are Well within the minimum requirements of various specifications, including military specifications such as, for example, MlL-L-7808B for Lubricating Oils, Gas Turbines, Aircraft.

' The-particular tetra-basic thioesters utilized in this invention are those derived from itaconic acid diester's.

'These compounds correspond to the formula:

.wherein R and R represent alkyl groups having from about 3 carbon atoms to about carbon atoms, and

preferably from about 4 to about 6 carbon atoms. The

R and R saturated hydrocarbon groups may contain the same number of carbon atoms or may vary within the limit of from 4 to about 6 carbon atoms. The total number of carbon atoms in one molecule of the tetra-ester utilized in my invention will vary from about 22 to 50 carbon atoms, and preferably from about 26-to 34 carbon atoms.

The tetra-esters of thio-di-itaconic acid corresponding to the general formula above are prepared by reacting 2 mols of the selected di-ester of itaconic acid with 1' mol of hydrogen sulfide in the presence ofa basic catalyst such as triethylamine. While this reaction will generally proceed Without a catalyst, increased reaction rate can be obtained by utilizing a relatively strong basic compound as catalyst. For example, such basic compounds as the organic bases, which include piperidine' and the secondary and tertiary aliphatic amines, and quaternary ammonium bases, all have been found suitable for increasing the reaction rate. It has also been found that the reaction with hydrogen sulfide may proceed more readily in the presence of a solvent which is inert to the reactants. Among the solvents which can be used are the low molecular weight aliphatic alcohols and ethers, as well as aromatic hydrocarbons such as benzene, toluene, xylene and the like.

The reaction in which the 2 mols of the selected diitaconic ester are reacted with hydrogen sulfide is believed to occur in two stages, in the first of'whicha mer capto derivative of the di-itaconate is formed, followed by a second reaction with the second di-ester molecule to form the thio-di-itaconic acid ester. I

For the purposes of the present invention, it has been found that the lower molecular weight esters of thio-diit'aconic acid having from 1 to 3 carbon atoms in the ester portion of the molecule, such as, for example, the tetramethyl ester, the di-methyl di-butyl ester, and the dimethyl di-amyl ester, do not possess satisfactory viscosity indices or pour points sufiiciently high to meet lubricating standards. On the other hand, the higher molecular weight esters, such as tetra-butyl, tetra-.amyl, or tetrahexyl, and mixed combinations of the same, have proven to be most satisfactory when compounded in the manner about 5% to about 2% of an oil-soluble acrylic acidpolymeric ester.

The acrylic acid polymeric ester utilized. in preparing these compositions may generally be represented by the formula:

wherein X represents a hydrogen atom or an alkyl group, R is a monovalentalkyl group containing from about 4 to 18 carbon atoms, and preferably from about 8 to 18 carbon atoms. Typical examples of the polymeric ester-s of the acrylic ester series which have been found suitable in preparing the compositions of the present invention are those prepared from the following alcohols: butyl, amyl, hexyl, cyclohexyl, decyl, cetyl and octadecyl. In addition, it has been found that the esters may be those of acrylic acid or methyl acrylic acid.

The polymers may be used as mixtures or in co-polymer form. A portion of this series of acrylic acid polymeric esters is manufactured by the Rohm and Haas Company, Philadelphia, Pennsylvania, and is commercially available under the trade name of Acryloids. The

Acryloids are believed to be co-polymers of the defined esters having a molecular weight varying between 5,000 and about 20,000 and having from 6 to 18 carbon atoms in the ester group, and are incorporated with various carriers, such as, neutral oils, transformer oils or other hydrocarbon base stocks.

In order to more fully understand the nature of this invention, and to illustrate the manner in which the improved compositions thereof are obtained, the following specific examples are provided:

Example 1 To 252 grams of di-n-butyl itaconate, gaseous hydrogen sulfide was added at room temperature in the presence of about 20 grams of triethylamine. The reaction vessel, a 500 ml., 3-necked, round-bottom flask, was provided with a mechanical stirrer and a thermometer. Hydrogen sulfide gas was introduced into the round-bottom flask by means of a dispersion tube which extended about of the way into the reaction mixture. During the initial addition of hydrogen sulfide, and continuously thereafter, the solution was rapidly stirred, with the temperature of the mixture being gradually increased by external heating to about 64 C. The reaction mixture was maintained at this temperature for about eight hours. The resulting reaction product was taken up in 250 ml. of toluene, neutralized with 10% sodium carbonate, and washed several times with hot water. The washings were discarded, and the neutralized reaction product vacuum distilled to remove solvent and volatiles. The fraction containing the desired ester was distilled under high vacuum, and yielded 183 grams of a crude, yellow, oily product. Color and odor improvement of the final product were obtained by treatment with 10% by weight of carbon black. The final product, tetra n-butyl thio-di (alphamethyl) succinate was a colorless liquid boiling from 224-226 C. at 160-170 microns of mercury pressure. The final product had the following properties:

To 9.8 grams of the foregoing final product, 0.2 gram of Acryloid 763 was added with stirring. Acryloid 763 comprises 33% of a copolymer prepared from 25 weight percent proportions of stearyl, cetyl, lauryl, and n-hexyl monomethacrylates dissolved in 150 neutral oil. The viscosity (cs.) of the resulting composition at 100 F. was 28.79, and 5.63 at 210 F. The final composition had a viscosity index of 143.2, a flash point of about 500 F., and a fire point of about 540 F.

Another portion of the tetra n-butyl thio-di (alphamethyl) succinate amounting to 9.5 grams was mixed with 0.5 gram (5%) of Acryloid 763. The resulting composition had a viscosity (cs.) at 100 F. of 31.52, and at 210 F. of 7.23. The viscosity index for this composition was 167.8.

Example 2 Following the procedure of Example 1, 206 grams of di-n-amyl itaconate were treated with a. slow stream of hydrogen sulfide in the presence of 20 grams of triethylamine. The temperature of the reaction mixture rose slowly to about 45 C., and remained at this temperature for approximately five hours, during which time hydrogen sulfide was continuously passed into the solution. The temperature was then increased with external heating to about 58 C. and was maintained at this temperature for an additional six hours. The reaction product recovered, according to the method described in Example 1, amounted to 60 grams, had a pale yellow color and boiled in the range of from 234241 C. at 60 90 microns of mercury pressure. The final purified product, tetra-namyl thio-di (alphamethyl) succinate, had the following properties:

To 9.8 grams of the tetra-n-amyl thio-di (alphamethyl) succinate, 0.2 gram of Acryloid 763 was added. Acryloid 763 is believed to comprise 33% of the mixed polymerized acrylic acid ester dissolved in 150 neutral oil. The viscosity (cs.) of the resulting composition at 100 F. was 36.04, and 6.33 at 210 F. The final composition had a viscosity index of 143, a flash point of about 530 F., and a fire point of about 550 F.

To another portion of the tetra-n-amyl thio-di (alphamethyl) succinate, consisting of 9.5 grams, 0.5 gram of Acryloid 618 were added with mixing. The resulting composition had a viscosity (cs.) at F. of 52.89, and at 210 F. of 9.79. This composition had a viscosity index of 148.

Example 3 Following the procedure described in Example 1, 96.9 grams of di-n-butyl itaconate and 108.0 grams of di-namyl itaconate were treated with hydrogen sulfide in the presence of 20 grams of triethylamine. The temperature rose slowly to about 45 C., with hydrogen sulfide being added at this temperature for about five hours. The temperature of the reaction mixture was then increased to about 5 8 C. and maintained for an additional six hours at this temperature.

The reaction product was treated according to the method described in Example 1, with grams of product being obtained. The crude product was pale yellow in color and boiled in the range of from 240 to 251 C. at 450 microns of mercury pressure. The purified polyester, di-n-butyl di-n-amyl thio-di (alphamethyl) succinate, was a pale yellow oil having the following properties:

Example 4 To 9.8 grams of di-n-butyl di-n-amyl thio-cli (alphamethyl) succinate, 0.2 gram of Acryloid 794 was added. Acryloid 794 comprises 25% of a copolymer prepared by polymerizing equal proportions by Weight of stearyl, cetyl,

lauryl, and n-hexyl monomethacrylates dissolved inl 75% neutral oil. The final composition had the following viscosities' ((58. at 100 F., 34.76;v at: 210 F., 6.54. The product had a viscosity index of 143.4.

Example 5 In another composition prepared in a manner similar to that above described, OISQgram of Acryloid79l4iwas added to 9.5 grams of di-n-butyl di-n-amyl thio-di (alphamethyl) succinate, prepared according to the method of Example 3. Acryloid 794 comprises of the mixed polymers of acrylic esters dissolved in 75% neutral oil. The final composition had the following viscosities (cs.): at 100 F., 42.95; at 210 F., 8.71. The product had a viscosity index of 154.3.

Example 6 210 F. The product had a viscosity index of 139.5.

Example 7 To 9.5 grams of di-n-butyl di-n-amyl thio-di (alphamethyl) succinate, prepared according to the method described in Example 3, 0.5 gram of Acryloid 618 was added. Acryloid 618 comprises 13% of the mixed polymers of acrylic esters dissolved in approximately 87% 100 neutral oil. The resulting composition had a viscosity (cs.) of 50.13 at 100 F., and 9.76 at 210 F. The viscosity index of the final composition was 151.5.

Example 8 A lubricating composition was prepared by adding to 9.8 grams of di-n-butyl di-n-amyl thio-di (alphamethyl) succinate, prepared according to the method of Example 3, 0.2 gram of Acryloid 710. Acryloid 710 comprises 38% of a copolymer prepared by polymerizing equal proportions by weight of stearyl, cetyl, lauryl, and n-hexyl monomethacrylates dissolved in 150 neutral oil. The viscosity (cs.) of the resulting composition was 33.21 at 100 F., and 5.99 at 210 F. The product had a viscosity index of 133.8.

Example 9 A lubricating composition was prepared by adding to 9.8 grams of di-n-butyl di-n-amyl thio-di (alphamethyl) succinate, prepared according to the method of Example 3, 0.2 gram of HF 825. HF 825 contains 55% of the acrylic polymeric esters dissolved in transformer oil. The viscosity (cs.) of the final composition was 34.58 at 100 F., and 6.51 at 210 F. The final composition had a viscosity index of 128.6.

Although no published advertising literature is available describing the Acryloids, it is known that in January 1956 and for a period prior to the foregoing date that the Acryloids listed below had the composition specified:

Acryloid 618--contains approximately 13% of a copolymer having a molecular weight of between 5,000 and about 20,000, prepared from 25 weight percent proportions of stearyl, cetyl, lauryl, and n-hexyl monomethacrylates dissolved in 100 neutral oil.

Acryloid 710-contains approximately 38% of a copolymer having a molecular weight of between 5,000 and about 20,000, prepared from 25 weight percent proportions of stearyl, cetyl, lauryl, and n-hexyl monomethacrylates dissolved in 150 neutraloil.

Acryloid 763-contains approximately 33% of a copolymer having a molecular weight of between 5 ,000 and about 20,000, prepared from 25 weight percent proportions of stearyl, cetyl, lauryl, and: n-hexyl monomethacrylates dissolved in 150 neutral oil.

Acryloid 794contains approximately 25% of a. co-.

polymer having a molecular weight of between 5,000 arid about 20,000, prepared from 25 weight percent proportions of stearyl, cetyl, lauryl, and n-hexyl monomethacrylates dissolved in 150 neutral oil.

The Acryloids defined above are currently available under the same designation and have the same composition as that specified at least as early as January 1956.

It will be noted that in all of the foregoing lubricating compositions, viscosity indices for the final compositions were substantially within the minimum required ranges of the specification grade lubricants set forth in the fol- In the foregoing table the lubricating oils 10W30 and SW20 represent commercial retailed specification grade lubricants.

The compositions described herein are suitable as lubricants in conventional internal combustion engines, as well as in turbine type engines. If desired, the compositions of the present invention may be blended with other suitable hydrocarbon oils, including mineral oil stocks, as well as other synthetic hydrocarbon oils. The compositions may include, without adversely affecting the lubricating characteristics, such additives as anti-oxidants, extreme pressure agents, stability agents, metal deactivators, and the like.

While the present invention has been described with respect to certain examples of the same, it is to be understood that the invention is not limited by the same, but is limited in scope only by the claims appended hereafter.

What I claim is:

1. A normally liquid lubricating composition comprising a major portion of a tetra ester of thiodi-itaconic acid having the formula wherein R and R represent saturated hydrocarbon groups having from about 4 to 6 carbon atoms, and a minor portion, sufi'icient to improve the viscosity characteristics of the tetra ester, of an oil-soluble copolymer having a molecular weight from 5,000 to 20,000 prepared from 25 weight percent proportions of stearyl, cetyl, lauryl, and n-hexyl monomethacrylates.

2. A normally liquid lubricating composition comprising from about to about 98% by weight of the tetra alkyl ester of thiodi-itaconic acid having the formula wherein R and R represent saturated hydrocarbon groups having from 4 to about 6 carbon atoms, and from 5 to about 2% by weight of an oil-soluble copolymer having a molecular weight of from 5,000 to 20,000 and prepared from 25 weight percent proportions of stearyl, cetyl, lauryl, and n-hexyl monomethacrylates.

3. A normally liquid lubricating composition as claimed in claim 1, wherein R and R represent hexyl claimed in claim 1, wherein R represents an amyl group, groups. and R represents a butyl group. i

4. A normally liquid lubricating composition as References Cited in the file of this patent 213313;? in claim 1, wherein R and R represent amyl 5 UNITED STATES PATENTS 5. A normally liquid lubricating composition as 2,503,401 Mattano et a1 Apr. 11, 1950 claimed in claim 1, wherein R and R represent butyl 2,668,847 Newton Feb. 9, 1954 groups. 2,683,119 Smith et al. July 6, 1954 ,6. A normally liquid lubricating composition as 10 2,737,525 Mulvaney et al Mar. 6,1956 

1. A NORMALLY LIQUID LUBRICATING COMPOSITION COMPRISING A MAJOR PORTION OF A TETRA ESTER OF THIODI-ITACONIC ACID HAVING THE FORMULA 